There are many industrial processes which require the separation of materials of diverse weights. One such process involves the separation of the composite materials of scrap insulated wire for recycling. In the telecommunications industry this wire is usually composed of an elongated, non-ferrous, conductive metal such as copper or aluminum covered with a layer of plastic or fibrous insulation. Where these wires are to be recycled they are typically passed through a granulator which cuts them into pieces. The cut pieces are then fed to a separator which separates the metallic from the non-metallic components. The recovered metal may then be recast and drawn into new wire.
Separators used in the just described process often include one or more gravity tables such as those shown in the systems disclosed in U.S. Pat. Nos. 3,074,653 and 3,823,820. Other separators employ impact mills as exemplified by U.S. Pat. No. 3,749,322, or hammer mills in conjunction with sink separation means as shown in U.S. Pat. No. 3,582,004. Some other separators include fiber-dust separation means in conjunction with granulators as shown in U.S. Pat. No. 3,941,684. Still another type separator has been used in separating carbon particulates of relatively light weight, porous structures, as well as those of relatively flat configuration, from particulates of heavier or more rounded shape. With this latter type the material is poured into a hopper while blowing air through the streaming material thereby causing the lighter and flatter carbon particulates to be blown into an adjacent hopper.
The just described separators can be effective in separating the metallic components of the scrap wire from the non-metallic except for the materials of very small sizes such as those measuring less than some 25 mils which are often termed "superfines". The prior art separators have been largely ineffective in separating these. Thus, it is a common practice today to make no attempt at separating the components of superfines but rather to discard them as waste.
Separation of superfines is difficult because of the tendency of their metallic and non-metallic components both to become readily airborne. For example, where gravity tables are used air forced upwardly through the tables causes the metallic and non-metallic components of superfines to become an airborne mixture. This same adverse effect also occurs where air is blown across the top of a materials supporting table and through a screen. The use of screens or sieves themselves is also impractical because of their tendency to become clogged when superfine materials are passed therethrough due to the required smallness of the screen interstices.
In addition to the foregoing problems in separating superfines are those associated with changing conditions in the separation process itself. One of these is the varying materials input rates which a superfine separator must often handle. This may be caused by any one of several factors including changes in line speed and changes in recirculation rates of the coarse and fine materials as back to gravity tables or choppers for conventional separation or rechopping. The character of the input product itself may also vary from time to time such as where different types or sizes of wires or cables are introduced which produce different proportions of coarse, fine and superfine materials. These dynamic conditions seriously complicate attempts to solve the previously described problems presented in separating superfines. The present invention therefore is directed at overcoming these problems by providing methods and apparatuses which are workable and effective in separating finely sized materials of diverse weights such as superfines.